Latch-up is a type of short circuit that occurs in an integrated circuit (IC). It is a failure condition characterized by runaway current railing (i.e., creation of a low-impedance path between power supply rails of the IC) due to bipolar amplification of electron-hole pairs. The p-n junction formed between active devices and the substrate, which are normally reverse biased, can become forward biased due to, for example, the absorption of cosmic radiation by the substrate. Such events (radiation-induced latch-up or Single-event Latch-up) cause a short circuit of current flow between power and ground rails that is typically well localized (i.e., within a few microns) to the vicinity of radiological absorption.
Errors caused by latch-up may be characterized as hard errors or soft errors. Soft errors may be resolved by a power reset or power cycle while hard errors are more catastrophic and permanent, tending to result in railing current, severe voltage droop, and thermal overload. Soft errors may become hard errors if they are left undetected and unmitigated, such as when power is not interrupted in the affected regions or components to reset the latch-up condition.